The present invention relates to a steering wheel having an airbag device for protecting an occupant from an impact applied from the front of a vehicle.
Japanese Laid-Open Patent Publication No. 2004-284414 discloses such a steering wheel, which includes a metal core, an airbag device, and a plurality of horn switch mechanisms. The metal core consists of the framework of the steering wheel. The airbag device is formed by assembling a pad portion, an airbag, and an inflator into a bag holder. The airbag device is arranged substantially above the metal core. The horn switch mechanisms are located between the airbag device and the metal core. When the airbag device is pressed down, the horn switch mechanisms activate the horn device.
When an impact is applied to a vehicle having the steering wheel from the front, the inflator of the airbag device discharges inflation gas to inflate the airbag. The inflation of the airbag breaks the pad portion. The airbag passes through the pad portion to be inflated between the steering wheel and the driver. The inflated airbag reduces the impact received by the driver.
The horn switch mechanisms are arranged between the bag holder and a metal horn plate attached to the metal core. Each horn switch mechanism has fixed members, movable members, urging members (load springs for the horn), and bolts. The fixed members include fixed contact portions and resin fixed supports supporting the fixed contact portions, and are supported by the horn plate. The movable members include movable contact portions and resin movable supports supporting the movable contact portions, and are supported by the bag holder. The load springs for the horn are located between the fixed members and the movable members, and urge the movable contacts upward away from the fixed contacts. The bolts allow the movable members to move substantially downward, thereby separating the movable contacts and the fixed contacts from each other.
When the driver presses down the airbag device of the steering wheel, the airbag device is moved toward the horn plate against the urging force of the load springs for the horn, together with the movable members and the bolts of the horn switch mechanisms. This causes the movable contact portions to contact the fixed contact portions, activating the horn device. In the airbag-equipped steering wheel disclosed in Japanese Laid-Open Patent Publication No. 2004-284414, the airbag device activates the horn device. This complicates the structure and increases the number of components.
Accordingly, the following configuration may be employed. As shown in FIG. 24, a metal core 49 includes a core body 52 and a holding portion 57 located substantially above the core body 52. The holding portion 57 has a through hole 55. An elastic member 56 is provided between the holding portion 57 and the core body 52 and in the vicinity of the through hole 55. A bag holder 51 is electrically connected to a horn device 62.
Horn switch mechanisms 50 each include a metal support member 58, an urging member 53, and a movable contact portion 54. The support member 58, the urging member 53, and the movable contact portion 54 are unitized before being installed in the bag holder 51. The support member 58 supports the bag holder 51 such that the bag holder 51 can move substantially in the up-down direction. The upper end face of the support member 58 forms a fixed contact portion 61. A locking groove 63 is formed in the lower end of the support member 58. The urging member 53 urges the bag holder 51 substantially upward and away from the metal core 49. The movable contact portion 54 moves together with the bag holder 51. This causes the movable contact portion 54 to contact the fixed contact portion 61, activating the horn device 62. The support member 58 attached to the bag holder 51 is inserted into the through hole 55 of the holding portion 57, and the elastic member 56 is engaged with the locking groove 63, so that the horn switch mechanism 50 is fastened to the holding portion 57 of the metal core 49.
In a normal state, in which the airbag device is not pressed down, the movable contact portion 54 is separated substantially upward from the fixed contact portion 61 of the support member 58. At this time, the contact portions 54, 61 are in a non-conductive state, and the horn device 62 does not operate. In contrast, when the airbag device is pressed down, the movable contact portion 54 is moved substantially downward together with the bag holder 51. This causes the movable contact portion 54 to contact the fixed contact portion 61, activating the horn device 62.
The support member 58 is locked to the metal core 49 and supports the bag holder 51 such that the bag holder 51 is movable in up-down direction relative to the metal core 49. The support member 58 also functions as the fixed contact portion 61. Therefore, the horn plate disclosed in Japanese Laid-Open Patent Publication No. 2004-284414 can be omitted. This reduces the number of the components and simplifies the structure.
In the above illustrated structure, the airbag-equipped steering wheel is attached to the metal core 49. Thus, when multiple horn switch mechanisms 50 installed in the bag holder 51 are fastened to the metal core 49, the support member 58 of each horn switch mechanism 50 is inserted into the through hole 55 of the holding portion 57 against the urging force of the elastic member 56. The insertion of the support member 58 into the through hole 55 deforms the elastic member 56 toward the outside of the support member 58. When the support member 58 is inserted to a position where the locking groove 63 is aligned with the elastic member 56, the elastic member 56 enters the locking groove 63 due to its own elastic force, and the support member 58 is locked to the metal core 49. This procedure is performed for each horn switch mechanism 50. When removing the airbag-equipped steering wheel from the metal core 49, the elastic member 56 is deformed with a tool, thereby moving the support member 58 away from the locking groove 63. When the elastic member 56 is removed from the locking groove 63, the spring force of the urging member 53 urges the support member 58 substantially upward so that the support member 58 comes off the through hole 55.
Japanese Laid-Open Patent Publication No. 2002-2433 discloses a configuration in which a single elastic wire is used for multiple through holes 55 to form the elastic member 56. According to this method, by moving the elastic wire to a disengaging position, the elastic wire, which is engaged with multiple support members 58, is disengaged at once. However, this method requires that the entire elastic wire be moved by an operation at one position. This complicates the structures for engaging and disengaging of the elastic wire. Also, the size of the elastic member 56 needs to be relatively large, and a space for allowing the elastic member 56 to move is required. On the other hand, as the functionality of steering wheels has been improved, it has become difficult to provide a sufficient space in the steering wheel.
Japanese Laid-Open Patent Publication No. 2004-268899 discloses a method for arranging an elastic member 56 in each of a plurality of through holes 55. Although this method reduces the space for the elastic member 56, the number of steps for removing the elastic members 56 from the support members 58 is increased in accordance with the number of the through holes 55. This makes the removal of the elastic members 56 troublesome.